1. Field of the Invention
This invention relates to the maintenance of air core cables such as air core plastic insulated telephone cables and more particularly, to a method and apparatus for treating air core cables. The apparatus of this invention includes a treatment tank for containing a treatment liquid, with an air space provided between the surface of the liquid and the top of the tank, a cable block applied to a segment of the cable, in order to isolate a length of the cable to be treated and an air application fitting and at least one liquid application fitting applied to the cable in spaced relationship over windows cut in the cable, for introducing air and liquid into the cable and treating the cable pairs inside the cable. The method of this invention includes the steps of isolating a segment of cable to be treated by blocking one end of the segment to be treated, cutting a pair of spaced windows in the cable and applying an air application fitting to one of the windows and a liquid application fitting to the other window, and pumping air and liquid in sequence from the treatment tank through the air application fitting and the liquid application fitting, respectively, to treat the cable pairs in the air core of the cable.
2. Description of the Prior Art
One of the problems realized in maintaining the many miles of air core cables such as air core plastic insulated telephone cables which have been laid over the years, is that of water intrusion, corrosion and galvanic action which takes place due to the presence of dissimilar metals in the cables. These actions produce undesirable electrical shorting of the cable pairs in the cable core and cause noise, interference and cross-telephone conversations in telephone lines which are served by the cable. Various techniques have been used to alleviate this problem, including the pumping of liquids and gases such as air and nitrogen through the cable to clear the cable of water and dry the telephone cable pairs. Various types of compounds such as copper sulfate and sulfuric acid are also formed in the cables and water intrusion changes the capacitance of the cable, which increases the noise level in telephone conversations. This problem is further complicated by the fact that many air core cables include a plastic outer sheath, an intermediate liner constructed of a metal such as copper, aluminum or steel metal and an optional plastic inner sheath, which contains the cable pairs. Under circumstances where the inner plastic sheath is worn, pitted or otherwise damaged to facilitate water intrusion to the metal jacket, or where no plastic inner sheath is placed in the cable, the copper, aluminum or steel oxidizes and forms compounds which are detrimental to the life and service of the cable pairs located in the air core cable.
Accordingly, it is an object of this invention to provide a new and improved method and apparatus for cleaning and treating air core cables and air core plastic insulated telephone cables in particular, to eliminate or minimize shorts, crosses and grounds in the cable pairs and to shield against galvanic action.
Another object of this invention is to provide a new and improved method and apparatus for treating air core plastic insulated telephone cables by removing water and moisture from the cables and cleaning the cables and sheaths of conductive corrosion which interferes with the transmission of electric current through the cable pairs.
Yet another object of this invention is to provide a method and apparatus for treating air core plastic insulated telephone cables to seal pin holes in the cable sheaths, prevent further intrusion of water into the cables and renew the flexibility of the insulation, as well as to reinsulate bare spots in the cable pairs which are caused by corrosion.
Still another object of the invention is to provide a new and improved method and apparatus for treating and internally repairing air core telephone cables of substantially any size along a cable path of up to about 1200 feet, including air core telephone cables characterized by non-filled splices.
Yet another object of the invention is to provide a method and apparatus for treating air core cables such as air core plastic insulated telephone cables with air or nitrogen in a first step and a low viscosity, light demoisturizing insulating and cleaning oil as a treating agent, in a second step.
Still another object of the invention is to provide a new and improved method and apparatus for treating air core telephone cables, which method and apparatus is cost-effective and can be accomplished for about one-fifth of the replacement cost of the cable.